This application relates to a vane pump wherein a cam ring rotates with the vanes, and wherein an under vane pressure is provided with structure to increase the force holding the vane against the cam ring.
Vane pumps are known, and typically include a rotor driven to rotate. The rotor carries a plurality of vanes that are biased outwardly of under vane slots, and against an inner periphery of a cam ring. As the rotor rotates, fluid in chambers between the vanes is moved from an inlet toward an outlet.
One type of vane pump has a rotating cam ring. The cam ring is caused to rotate with the vanes, typically by a frictional contact between the vane and the cam ring. This type of vane pump raises challenges, in that it is sometimes difficult to ensure the cam ring rotates at a sufficient speed.
It is known in vane pumps to provide an under vane pressure to hold the vane outwardly against the inner periphery of the cam ring. However, this has not always proven sufficient to move the cam ring at the desired speed in a rotating cam vane pump.
In a balanced vane type of vane pump without the rotating cam ring, but rather a fixed cam ring, it is known to have an under vane pressure wherein a back pressure valve ensures the pressure in the under vane chamber is high. However, this concept has never been applied to a rotating cam vane pump.